Which battery should I buy? - R21-EC

[Boris the Tug]

I have a 2009 RC21-EC I bought used last year and need to replace the house battery.

The existing house battery in the boat is a Moto Master Natulilus with 625a/70 (model 010-2499-8)
The existing starting battery is an Armor Plate Marine Starting (group size APSM24-625)

Those are the markings on each battery, sorry I don't know what to look for specifically.

The seller said the starting battery was replaced when I bought the boat (but not sure if it was brand new or not).

The house battery is dead and I need to replace it. I would also replace both batteries at the same time if that's recommended.

Could someone help me understand my battery purchase options:
What things should I consider?
Brand?
Cranking amps?
Group size?
Should I replace both at the same time?
AGM?

Any help is much appreciated. Thank you.

 

[Capt’nKarl]

Good afternoon Boris. You’ll likely get more answers to this question than almost any other and they’ll all be right. Battery selection has so many factors to consider and my needs may not be your needs. However here’s where I’ll start. I too have a 2009 21EC that I bought 6 years ago. The original equipment had 12 Volt A/C so I had 2 additional batteries to contend with. All 4 batteries, 2 for the A/C, 1 house and 1 starter battery needed to be replaced when I bought the boat. The 12 Volt A/C did NOTHING to cool the cabin down in our Florida weather so...out they went. We use our boat I so many conditions and this will be a major factor in your selection for battery replacement. We tend to stay out for 1-2 days at a time then find a marina slip so we can shower, eat good meals and run our 110 Volt A/C on shore power. When at anchor we actually use very little battery power. We have solar lights we use for our anchor light, reading lights and cockpit lights. We do run the fridge 24/7 but find it consumes very little battery power. We have underwater lights we use on occasion and listen to music a lot. Still, with all this we have never come close to losing power from our $95.00 Walmart Marine batteries. It’s been 6 years since I bought these Walmart batteries and they are still going strong. I do have a battery monitor and a compact 12 Volt Nekteck emergency starting device but have yet needed to use it. So, for me I don’t invest a lot in my batteries. So far so good. Battery numbers. Marine MAXX-24DC Deep Cyclling Power, Group Size 24DC, Selection Number 93. 690 marine cranking Amps. Starter battery. Ever start Marine Selection Number 91. I’m watching my batteries close now since they are over 5 years old but I’ll replace them with similar types.
Cheers,
Karl

 

[knotflying]

Ditto what Karl stated. Go Walmart flooded and you will be fine. Nine times out of ten it's not the battery that is the problem, it is the people using them that kill them.

 

[greenghost45]

Before getting our R21EC, we had a sailboat for about 15 years and spent 2 years cruising Mexico, mostly off the hook. So we learned to live off grid. The previous post is right; it is mostly about the folks using the batteries, rather than the batteries. If you replace the batteries in pairs, and get 2 deep cycle batteries, you will be better off. And I know I will likely get criticized, but you could use both batteries concurrently, while carefully monitoring state of charge. This will extend the life of the house battery, compared to using just one battery for the house. Just be careful not to discharge below a resting voltage of about 12.05. The truth is you should never discharge any battery below 50% charge, and 60 is better. If you are worried about "what if?", then get one of those emergency boost batteries. Besides Walmart, Costco also has good prices for deep cycle batteries. Solar panels are very cheap these days. A panel mounted on top of the Bimin could extend your battery life too.
https://www.bing.com/images/search?q=12 ... &FORM=IGRE

 

[Boris the Tug]

Thank you VERY much for the insight. I'm running stereo and lights while anchored, and I think that's about it. No fridge (maybe eventually) and no a\c. Have a generator for other stuff if needed.

I'm on board with the Walmart batteries. Are these correct?

House battery:
https://www.walmart.com/ip/EverStart-Ma ... /139801236

Starter battery (out of stock):
https://www.walmart.com/ip/EverStart-Le ... S/49988441

Did I get that right? If not, these are all the group 24 marine batteries at Walmart. Also, any alternative for the out of stock MS above?
https://www.walmart.com/ip/EverStart-Le ... S/49988441

I appreciate you making this easier, great to hear from experienced R21 owners!

 

[knotflying]

Any Flooded will work and the price difference between stores is minimal. I bought my last flooded engine cranking battery at O'Riely's because Walmart was out.

 

[greenghost45]

My R21EC battery box will not take batteries bigger than a group 24, so if yours has the same battery box, the group 24 is correct. Personally, I would go with 2 deep cycle, group 24. A small diesel will happily start on a deep cycle battery in the temperate weather (i.e. above freezing) that Ranger tugs are likely to see on the water. With 2 deep cycles, you can alternate house batteries and prolong their life. Or as I already suggested, use both batteries at the same time and carefully monitor state of charge, which you should be doing anyway. Which brings up another point; battery switches. If you are doing the house/starting separation thing, then you HAVE to remember to switch back and forth. Switching batteries with a running engine can be a dicey business. Most alternators do NOT like a "no battery connected" situation, even for a few seconds. It can damage diodes. If your battery switch has a dead spot between positions, or if you accidentally select the off position, you may damage the alternator. And, you have to remember to switch back and forth when you stop and start the engine. If you forget to while at anchor, the starting battery will not like the draw down and probably not last long.

On my sailboat, I wired in a battery combiner. It automatically switched from both batteries to house only, when the engine was stopped. And switched back to both batteries, when the engine was started. It was wonderful, I never touched the battery switch for years! But it did add gear and complexity, which I am not going to add to my Ranger.
For my Ranger, I plan to use both batteries at all times and just monitor voltage and state of charge carefully. Sorry fo the long post, but I think this subject is worthwhile digging in a little deeper.

 

[Capt’nKarl]

Greenghost45 and Knotflying both speak rightly.
Karl

 

[Pilotnavigator]

I stay on anchor for several days without moving and needed more house amp hours. So changes out the factory 24s with 27s AGM mounted on their ends. Fits well. Also added two more house for a total of three group 27s in the rear bench seat.

 

[Capt’nKarl]

This post goes exactly with how people use their battery banks differently.Whats right for me may not be right for you. When I made my post I mentioned the age of my batteries and knew they were nearing the end. Well, we went out and spent the night at anchor, played the stereo, had the deck lights on for a while,the fridge, played with the spotlight and used the underwater lights a short time. Went to sleep with battery monitor showing 12.3volts. Had peaceful dreams. Woke up in the morning to dead batteries. Thankfully I had recently purchased a Necteck portable power pak. Hooked it up and instant start. Saved the day! Now I know I need new batteries.
Cheers,
Karl and Sara